1. Technical Field
The present disclosure relates to communication systems and methods and to advantageous devices, systems and/or components for use in association therewith.
2. Background Information
A network, e.g., a local area network (LAN), typically includes a plurality of personal computers and/or other devices (e.g., processors, servers, IP telephones, cameras, and the like) that are interconnected via network transmission media (e.g., wires and/or cables) and/or other network devices (e.g., hubs, switches, patch panels and the like). Personal computers and other network devices have traditionally received power from wall mounted outlets that supply 120 VAC (voltage alternating current). However, it has been determined that the need to receive power from wall mounted outlets can be eliminated, or at least reduced, in certain instances. One such circumstance involves devices that are connected to networks.
More particularly, devices that are connected to network transmission media (e.g., Ethernet transmission media) may be capable of receiving sufficient power over the network such that the device may be powered without causing intolerable effects to data transmitted via the transmission media. For example, U.S. Pat. No. 6,218,930 issued to Katzenberg et al. discloses an apparatus and method for use in supplying power via a network transmission medium.
Consequently, systems are now being developed for providing power over a network transmission medium, e.g., an Ethernet transmission medium. One such type of system is the “Power Over Ethernet 6000 Midspan Series” (referred to hereafter as the “Midspan Series”), manufactured by PowerDsine (Hod Hasharon, Israel). The “Midspan Series” is adapted to be installed between a power source and a patch panel. As is known in the art, a patch panel is a type of midspan device that is often used in making connections between transmission media, devices and/or combinations thereof. For example, a patch panel may be used to connect network computers to each other and/or to other network device(s) that connect to a wide area network, e.g., the Internet. Some patch panels are similar to static switchboards and include a plurality of sockets or ports that are adapted to receive plugs disposed at ends of short cables of network transmission media (sometimes referred to as patch cables or patch cords). Such patch panels enable devices to be connected to one another by virtue of plugging the plug ends of patch cords into appropriate port(s) of the patch panel. Devices may be disconnected from one another by unplugging such patch cords from the patch panel. Some other types of patch panels (sometimes referred to as wireless patch panels) allow connections to be made and broken in response to operator-controlled switches or another type of operator-controlled input device (and/or in response to another type of device capable of providing input commands to control the wireless patch panel).
Patch panels are often mounted in rack systems, sometimes referred to as “computer racks” or simply “racks,” to facilitate organization and management of the patch panels and/or the network transmission media (e.g., unshielded twisted pair (UTP) cables) which are routed to the ports of the patch panel (commonly located at the front and rear of the patch panel). For cable management purposes, the patch cords are often drawn toward one or the other side of the patch panel at the front of the rack system and, from there, routed to the desired network device and/or network communication location.
In addition, as is known in the art, many local area networks use unshielded twisted pair (UTP) cables and UTP-based systems as network transmission media. This is due in part to the large installed base of UTP cables/systems, the cost parameters associated with such cables/systems, and the ease and experience associated with installation of such systems. The demands on networks using UTP systems have increased (e.g., 100 Mbit/s and 1000 Mbit/s transmission rates) over recent years. This evolution in the marketplace has led to a desire for UTP systems that provide higher system bandwidth with lower noise. As is known in the art, a received signal generally consists of a transmission signal that is modified by various distortions. The distortions and additional unwanted signals are typically inserted by the transmission system somewhere between transmission and reception. The unwanted signals are referred to as noise, which can be a major limiting factor in the performance of a communication system, e.g., due to data errors, system malfunctions and/or loss of desired signal(s).
One category of noise is referred to as crosstalk noise. Generally speaking, crosstalk noise occurs when a signal from one source is coupled to another line. Crosstalk noise is thus a type of electromagnetic interference (EMI) which occurs through the radiation of electromagnetic energy, as described by Maxwell's wave equations (in unbounded free space a sinusoidal disturbance propagates as a transverse electromagnetic wave). One type of crosstalk noise is referred to as near end cross talk (NEXT) noise. NEXT noise is the effect of near-field capacitive (electrostatic) and inductive (magnetic) coupling between source and victim electrical transmissions. NEXT increases the additive noise at the receiver and therefore degrades the signal-to-noise ratio (SNR).
There are known methods for coupling DC power upon a four pair UTP cabling system. One method is to couple DC power on lines that do not transmit data signals. For example, 10BASE-T and 100BASE-T systems transmit on only two pairs of wires. This method does not involve utilizing low noise circuitry concepts of noise balance because the data signals are not negatively effected by the DC power coupling. Another method is to couple DC power on lines that do transmit data signals. For example, 1000BASE-T utilizes all four wire pairs for data transmission. For systems that couple power onto data transmission lines, it is advantageous to minimize the potential negative effect to the data signals. For example, coupling of DC power onto a high speed data line that is intended to perform at or above minimum category 5e performance levels will require a coupling approach that introduces minimal noise to the circuitry. If the design introduces too much noise, substantial data loss can occur.
The desire for higher system bandwidth and lower noise has led to the development of industry standards that require higher system bandwidth and lower noise connecting hardware. For example, the ANSI/TIA/EIA 568B.2 and ANSI/TIA/EIA 568B.2-1 standards define electrical performance requirements for category 5e and category 6 systems, respectively. Category 5e systems utilize the 1–100 MHz frequency bandwidth range. Category 6 systems utilize the 1–250 MHz frequency bandwidth range. Exemplary data systems that utilize the 1–250 MHz frequency bandwidth range are IEEE Token Ring, Ethernet 100Base-T and 1000Base-T. Further specifications have been developed to define electrical requirements for systems that provide power over high speed and low noise UTP cabling. For example, IEEE 802.3an defines electrical requirements for devices that deliver power over Ethernet and devices that receive power delivered thereby. TIA 568B.2-6 (draft) defines electrical and structured cabling requirements for delivering power on unshielded twisted pair (UTP) cable having four wire pairs.
FIG. 1A is a representation of a UTP cable connected to a RJ45 telecommunication plug. The UTP cable has four wire pairs, designated 1–4. The plug has eight contacts, designated 1–8, as required for a FCC part 68 RJ45 telecommunication plug. The four wire pairs are connected to the eight contacts in accordance with the requirements of T568B. More particularly, the wires of wire pair 1 are connected to contact positions 4 and 5, respectively. The wires of wire pair 2 are connected to contact positions 1 and 2, respectively. The wires of wire pair 3 are connected to contact positions 3 and 6, respectively. The wires of wire pair 4 are connected to contact positions 7 and 8, respectively. The contacts may be used, for example, for tip (positive voltage) and ring (negative voltage) signal transmissions.
Transposition or twisting of a transmitting wire pair helps minimize crosstalk generated in the UTP cable. However, significant crosstalk can occur at the end of the cable where the wire pairs are not twisted. Crosstalk can also occur at the plug contacts connected to the wire pairs. The magnitude of such crosstalk generally increases as the system speeds or system transmission frequencies increase. Thus, while early industry standards called for connecting hardware to provide NEXT loss of less than −36 dB at 16 MHz, category 6 systems are required to provide −54 dB at 100 MHz and −46 dB at 250 MHz.
Notwithstanding efforts to date, further devices, systems and methods for use in providing power over network transmission media are desired. In addition, devices, systems and methods that can be used in addressing the demand for high bandwidth and low noise while providing power over network transmission media are also desired. These and other objectives are met by the apparatus, systems, devices and methods described herein.